Detecting device, power receiving device, contactless power transmission system, and detecting method

ABSTRACT

Disclosed herein is a detecting device including a coil electromagnetically coupled to the external, a resonant circuit that includes at least the coil, and a detecting section that superimposes a measurement signal for measuring the Q-factor of the resonant circuit on a power transmission signal transmitted to the coil in a contactless manner and removes the power transmission signal from an alternating-current signal obtained by superimposing the measurement signal on the power transmission signal. The detecting section measures the Q-factor by using the alternating-current signal from which the power transmission signal is removed.

BACKGROUND

The present disclosure relates to a detecting device, a power receivingdevice, a contactless power transmission system, and a detecting methodto detect the existence of a conductor such as a metal.

In recent years, the contactless power transmission system to supplypower in a contactless manner (wireless power feed) is being activelydeveloped. As the system to realize the wireless power feed, two kindsof techniques exist in a rough classification.

One is the electromagnetic induction system, already widely known. Inthe electromagnetic induction system, the degree of coupling between thepower transmission side and the power reception side is very high andpower feed with high efficiency is possible. However, the couplingcoefficient between the power transmission side and the power receptionside needs to be kept high. Therefore, the power transmission efficiencybetween the coils of the power transmission side and the power receptionside (hereinafter, referred to as the “inter-coil efficiency”) greatlydeteriorates when the distance between the power transmission side andthe power reception side is long or when there is positionalmisalignment.

The other is the technique called the magnetic resonance system. It hasa characteristic that the resonance phenomenon is aggressively utilizedand thereby even little magnetic flux is permitted as the magnetic fluxshared by the power feed source and the power feed target. In themagnetic resonance system, even when the coupling coefficient is small,the inter-coil efficiency does not deteriorate if the quality factor(Q-factor) is high. The Q-factor is an index representing therelationship between retention and loss of energy in a circuit havingthe coil of the power transmission side or the power reception side(indicating the intensity of the resonance of a resonant circuit). Thatis, axis alignment between the transmission-side coil and thereception-side coil is unnecessary and flexibility in the position anddistance of the power transmission side and the power reception side ishigh.

One of the important factors in the contactless power transmissionsystem is countermeasures against heat generation of a metal foreignsubstance. Whether the system is the electromagnetic induction system orthe magnetic resonance system, in contactless power feed, if a metalexists between the power transmission side and the power reception side,possibly an eddy current is generated in the metal and heat generationof the metal is caused. As countermeasures against this heat generation,a large number of techniques to detect the metal foreign substance havebeen proposed. For example, techniques using an optical sensor or atemperature sensor are known. However, in the detecting method using asensor, the cost is high when the power feed range is wide like in themagnetic resonance system. Furthermore, for example, in the case of thetemperature sensor, the output result of the temperature sensor dependson the thermal conductivity of the environments around it, which imposesdesign restrictions on the pieces of apparatus of the power transmissionside and the power reception side.

To address this, the following technique has been proposed.Specifically, whether or not a metal foreign substance is present isdetermined by monitoring change in a parameter (current, voltage, etc.)when the metal foreign substance encroaches between the powertransmission side and the power reception side. Such a technique cansuppress the cost without the necessity to impose design restrictionsand so forth. For example, Japanese Patent Laid-open No. 2008-206231(Patent Document 1) proposes a method in which a metal foreign substanceis detected based on the degree of modulation (information on change inthe amplitude and phase) in the communication between the powertransmission side and the power reception side. Furthermore, JapanesePatent Laid-open No. 2001-275280 (Patent Document 2) proposes a methodin which a metal foreign substance is detected based on the eddy currentloss (foreign substance detection based on the DC (direct current)-DCefficiency).

SUMMARY

However, in the techniques proposed by Patent Documents 1 and 2, theinfluence of a metal chassis of the power reception side is not takeninto consideration. Considering a charge to general portable apparatus,the possibility that some kind of metal (metal chassis, metal parts,etc.) is used in the portable apparatus is high and it is difficult todiscriminate whether change in a parameter is due to “the influence of ametal chassis or the like” or due to “interfusion of a metal foreignsubstance.” For example, in the case of Patent Document 2, it is unclearwhether the eddy current loss is caused in the metal chassis of portableapparatus or is caused due to interfusion of a metal foreign substancebetween the power transmission side and the power reception side. Asjust described, it cannot be deemed that the techniques proposed byPatent Documents 1 and 2 are capable of detecting a metal foreignsubstance with high accuracy.

There is a need for the present disclosure to detect a metal foreignsubstance existing near a coil without newly providing a sensor andenhance the accuracy of the detection.

According to an embodiment of the present disclosure, there is provideda detecting device including: a coil configured to beelectromagnetically coupled to an external; a resonant circuitconfigured to include at least the coil; and a detecting sectionconfigured to superimpose a measurement signal for measuring a Q-factorof the resonant circuit on a power transmission signal transmitted tothe coil in a contactless manner and remove the power transmissionsignal from an alternating-current signal obtained by superimposing themeasurement signal on the power transmission signal, the detectingsection measuring the Q-factor by using the alternating-current signalfrom which the power transmission signal is removed.

According to another embodiment of the present disclosure, there isprovided a power receiving device including: a coil configured to beused to receive power from an external; a resonant circuit configured toinclude at least the coil; and a detecting section configured tosuperimpose a measurement signal for measuring a Q-factor of theresonant circuit on a power transmission signal transmitted to the coilin a contactless manner and remove the power transmission signal from analternating-current signal obtained by superimposing the measurementsignal on the power transmission signal, the detecting section measuringthe Q-factor by using the alternating-current signal from which thepower transmission signal is removed.

According to still another embodiment of the present disclosure, thereis provided a contactless power transmission system including a powertransmitting device that wirelessly transmits power and a powerreceiving device that receives power from the power transmitting device,the power receiving device including: a coil configured to be used toreceive power from an external; a resonant circuit configured to includeat least the coil; and a detecting section configured to superimpose ameasurement signal for measuring a Q-factor of the resonant circuit on apower transmission signal transmitted to the coil in a contactlessmanner and remove the power transmission signal from analternating-current signal obtained by superimposing the measurementsignal on the power transmission signal, the detecting section measuringthe Q-factor by using the alternating-current signal from which thepower transmission signal is removed.

According to a further embodiment of the present disclosure, there isprovided a detecting method including: superimposing a measurementsignal for measuring a Q-factor of a resonant circuit including at leasta coil on a power transmission signal transmitted to the coil in acontactless manner by a detecting section included in a detectingdevice; removing the power transmission signal from analternating-current signal obtained by superimposing the measurementsignal on the power transmission signal; and measuring the Q-factor byusing the alternating-current signal from which the power transmissionsignal is removed.

According to the embodiments of the present disclosure, a metal foreignsubstance existing near the coil can be detected without newly providinga sensor and the accuracy of the detection is enhanced.

Furthermore, detection of a metal foreign substance with high accuracycan be realized on the secondary side without stopping powertransmission from the primary side to the secondary side.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic circuit diagram for explaining Q-factormeasurement used for detection of a metal foreign substance in anembodiment of the present disclosure;

FIG. 2 is a schematic circuit diagram showing a configuration example ofa power receiving device in a contactless power transmission systemaccording to a first embodiment of the present disclosure;

FIG. 3 is a circuit diagram showing part of an internal configurationexample of a transmission carrier removing filter portion in FIG. 2;

FIG. 4 is a graph showing a frequency characteristic example of theimpedance of the transmission carrier removing filter portion of FIG. 3;

FIG. 5 is a graph showing an example of the relationship between thefrequency and filter loss of the transmission carrier removing filterportion;

FIG. 6 is a graph showing a waveform example of a voltage V1 and avoltage V2 in FIG. 2;

FIG. 7A is a graph showing a spectrum characteristic example of thevoltage V1 and FIG. 7B is a graph showing a spectrum characteristicexample of the voltage V2;

FIG. 8 is a graph showing an example of the relationship between thefrequency and the Q-factor when the Q-factor of a power receiving coilis measured by using an LCR (inductance-capacitance-resistance) meter;

FIGS. 9A to 9C are circuit diagrams showing configuration examples of aresonant circuit;

FIG. 10 is a schematic circuit diagram showing a configuration exampleof a power receiving device in a contactless power transmission systemaccording to a modification example of the first embodiment of thepresent disclosure;

FIGS. 11A and 11B are circuit diagrams showing configuration examples ofthe resonant circuit;

FIG. 12 is a circuit diagram showing a configuration example of a powerreceiving device according to a second embodiment of the presentdisclosure;

FIG. 13 is a flowchart showing an operation example in Q-factormeasurement of a contactless power transmission system according to thesecond embodiment;

FIG. 14 is a flowchart showing an operation example (Q-factormeasurement result is transmitted) in Q-factor measurement of thecontactless power transmission system according to the secondembodiment;

FIG. 15 is a circuit diagram showing a configuration example of a powerreceiving device according to a third embodiment of the presentdisclosure;

FIG. 16 is an equivalent circuit diagram for the power transmissionfrequency of the power receiving device of FIG. 15;

FIG. 17 is an equivalent circuit diagram for the Q-factor measurementfrequency of the power receiving device of FIG. 15;

FIG. 18 is a flowchart showing an operation example in Q-factormeasurement of a contactless power transmission system according to thethird embodiment;

FIG. 19 is a flowchart showing an operation example (Q-factormeasurement result is transmitted) in Q-factor measurement of thecontactless power transmission system according to the third embodiment;

FIG. 20 is a graph showing a frequency characteristic example of theimpedance in a series resonant circuit; and

FIG. 21 is a graph showing a frequency characteristic example of theimpedance in a parallel resonant circuit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Examples of modes for carrying out the present disclosure will bedescribed below with reference to the accompanying drawings. In thepresent specification and the drawings, the constituent elementsubstantially having the same function or configuration is given thesame numeral and thereby overlapping description is omitted.

The description will be made in the following order.

1. Introduction

2. First Embodiment (detecting section: example including a resonantfrequency adjuster and a first frequency remover)3. Second Embodiment (separator: example in which a separator isprovided on the load side of a resonant circuit)4. Third Embodiment (frequency remover: example in which a secondfrequency remover is provided instead of a separator)

5. Others 1. Introduction

Embodiments of the present disclosure are a technique of measuring thequality factor (Q-factor) of a circuit including a coilelectromagnetically coupled to the external when power is fed from thepower transmission side (primary side) to charge the power receptionside (secondary side), and determining whether or not a metal foreignsubstance near the coil is present based on the measurement result ofthe Q-factor.

The Q-factor is an index representing the relationship between retentionand loss of energy and is generally used as a value representing thesharpness of the peak of the resonance (intensity of the resonance) of aresonant circuit.

The metal foreign substance covers a conductor such as a metal existingbetween the power transmission side and the power reception side and acircuit including an unintended coil. Conductors in a broad sense, i.e.semiconductors, are also encompassed in the conductor in the presentspecification. Hereinafter, detecting a conductor such as a metal and acircuit including a coil will be expressed also as “detecting aconductor and so forth.”

[Principle of Q-factor Measurement]

The principle of the Q-factor measurement will be described below withreference to drawings.

FIG. 1 is a schematic circuit diagram for explaining the Q-factormeasurement used to detect a metal foreign substance in the embodimentsof the present disclosure.

The circuit shown in FIG. 1 is one example of the most basic circuitconfiguration representing the measurement principle of the Q-factor (inthe case of magnetic field coupling). Although FIG. 1 shows a circuitincluding a series resonant circuit composed of a coil 5 and a capacitor4, various modes will be available as the mode of the detailedconfiguration as long as the configuration has the function of theresonant circuit. The Q-factor measurement of this resonant circuit is atechnique used also in a measurement instrument (LCR meter).

If e.g. a metal piece exists near the coil 5 as a metal foreignsubstance, magnetic field lines pass through the metal piece and an eddycurrent is generated in the metal piece. This looks, from the viewpointof the coil 5, as if the metal piece is electromagnetically coupled tothe coil 5 and a resistive load is imposed on the coil 5, and changesthe Q-factor of the coil (resonant circuit). Measuring this Q-factorleads to detection of a metal foreign substance (in theelectromagnetically-coupled state) existing near the coil 5.

The circuit used for the Q-factor measurement shown in FIG. 1 includes asignal source 1 including an alternating-current (AC) power supply 2that generates an AC signal (sine wave) and a resistive element 3, thecapacitor 4, and the coil 5. The resistive element 3 is equivalent todiagrammatic representation of the internal resistance (outputimpedance) of the AC power supply 2. The capacitor 4 and the coil 5 areconnected to the signal source 1 in such a manner as to form a seriesresonant circuit (one example of the resonant circuit). Furthermore, thevalue of the capacitance (C value) of the capacitor 4 and the value ofthe inductance (L value) of the coil 5 are adjusted so that the resonantcircuit may resonate at the frequency desired to be measured.

If the voltage between both ends of the coil 5 and the capacitor 4configuring the series resonant circuit is defined as V1 (one example ofthe voltage applied to the resonant circuit) and the voltage betweenboth ends of the coil 5 is defined as V2, the Q-factor of this seriesresonant circuit is represented by expression (1). R denotes the seriesresistance value at a frequency f. L denotes the inductance value and Cdenotes the capacitance value. When a relationship of voltageV2>>voltage V1 is satisfied, the expression can be approximatelyrepresented.

Error! Objects cannot be created from editing field codes.

The voltage V2 is obtained by multiplication of the voltage V1 by aboutQ. It is known that the series resistance value R and the inductancevalue L shown in expression (1) change due to the influence of theapproach of a metal or an eddy current generated in a metal. Forexample, when a metal piece approaches the coil 5, the effectiveresistance value R becomes larger and the Q-factor decreases. That is,the Q-factor and resonant frequency of the resonant circuit greatlychange due to the influence of the metal existing around the coil 5.Therefore, by detecting this change, the metal piece existing near thecoil 5 can be detected. Furthermore, this Q-factor measurement can beapplied to detection of a metal foreign substance inserted between theprimary side and the secondary side.

By detecting a metal foreign substance by using change in theabove-described Q-factor, the metal foreign substance can be removedwith high accuracy irrespective of whether the system is theelectromagnetic induction system or the magnetic resonance system. Inparticular, the Q-factor of the coil provided in apparatus of the powerreception side (secondary side) allows removal of the influence of ametal chassis on the coil and can be a parameter having high sensitivityto the metal foreign substance because the positional relationshipbetween the metal chassis of the apparatus of the power reception sideand this coil is almost fixed. That is, the Q-factor of the powerreception side is suitable for detection of the metal foreign substance.

[Outline of Present Disclosure]

However, when foreign substance detection by the Q-factor measurement isapplied to the secondary side, the power transmission signal from theprimary side is an obstacle to accurate measurement of the Q-factor ofthe secondary-side coil. If power feed (output of the power transmissionsignal) from the primary side is being performed at the time of Q-factormeasurement, high power is generated in the coil of the secondary sidedue to the magnetic field output from the primary side, which precludesnormal measurement of the voltage V2 of the Q-factor measurement signaland so forth.

The Q-factor of the secondary-side coil is measured by using thetechnique shown in FIG. 1 and applying a voltage (Q-factor measurementsignal) to the resonant circuit composed of this secondary-side coil anda capacitor. If this measurement is performed when power is beingtransmitted from the primary side, a voltage is generated in thesecondary-side coil due to the power transmission from the primary side.This results in an error in the Q-factor measurement. In general, thepower transmission is performed with high power and therefore theamplitude of the power transmission signal is much larger compared withthe Q-factor measurement signal. Thus, the measurement of the Q-factorcannot be accurately performed.

Therefore, to avoid this, the power transmission from the primary sideto the secondary side needs to be stopped via a complicated control flowand the Q-factor of the secondary side needs to be measured with thepower transmission stopped. For this purpose, a communication system andcontrol to perform communication between the primary side and thesecondary side and send a power transmission stop signal for everymeasurement of the Q-factor of the secondary side are necessary. Thiscauses problems of increase in the complexity of the control flow andhardware of the power transmitting device and the power receiving deviceand increase in redundant time in the Q-factor measurement attributed toit.

Furthermore, for example, also when plural power receiving devices existfor one power transmitting device, every time the Q-factor of one powerreceiving device is measured, even power feed to the other powerreceiving devices needs to be stopped.

To address such a problem, it will be effective to employ a method torealize foreign substance detection by Q-factor measurement in powerfeed by an improvement relating to the coil, such as providing a coilfor Q-factor measurement separately from the power receiving coil orincreasing the number of turns of the power receiving coil. However,possibly this method adversely affects the flexibility in the design ofthe apparatus of the power reception side and the cost after all.

So, the present disclosure proposes a technique to measure the Q-factoron the secondary side without stopping power transmission on the primaryside. In this technique, a Q-factor measurement signal is superimposedon a power transmission carrier (power transmission signal) with afrequency different from that of the transmission carrier and only theQ-factor measurement signal is extracted in Q-factor measurement(voltage measurement). Based on this, the Q-factor measurement isperformed simultaneously with the power transmission from the primaryside.

2. First Embodiment

In embodiments of the present disclosure, on an AC signal fed as powerfrom the power transmission side (hereinafter, referred to as the “powertransmission signal”), an AC signal for Q-factor measurement with afrequency different from that of the power transmission signal(hereinafter, referred to as the “Q-factor measurement signal”) issuperimposed. Furthermore, the Q-factor is measured by using the ACsignal obtained by removing the power transmission signal from the ACsignal resulting from the combining of two AC signals.

[Configuration Example of Power Receiving Device]

FIG. 2 is a schematic circuit diagram showing a configuration example ofa power receiving device in a contactless power transmission systemaccording to a first embodiment of the present disclosure.

A contactless power transmission system 100 includes a powertransmitting device 10 (primary side) including at least a powertransmitting coil 10A and a power receiving device 20 (secondary side).The power receiving device 20 is one example of the detecting device.

The power receiving device 20 includes a power receiving coil 21 (oneexample of the coil), capacitors 22 and 23, a rectifier 24, a load 25,and a detecting section 26 (one example of the detecting section) as oneexample.

In the power receiving device 20, one terminal of the power receivingcoil 21 and the capacitor 22 connected in parallel is connected to oneterminal of the capacitor 23 connected in series to this power receivingcoil 21, so that a resonant circuit is configured. This resonant circuitis connected to the load 25 via the rectifier 24. The inductance value(L value) of the power receiving coil 21 and the capacitance value (Cvalue) of the capacitors 22 and 23 are adjusted so that the resonantcircuit may resonate at the frequency for Q-factor measurement. Thepower receiving section is configured by the capacitors 22 and 23 andthe rectifier 24.

In the power receiving device 20, an AC magnetic field generated by thepower transmitting device 10 is received by the power receiving coil 21by e.g. a magnetic resonance system and the AC signal is extracted viathe resonant circuit including the power receiving coil 21 and thecapacitors 22 and 23. The extracted AC signal is converted to a DCsignal through rectification and smoothing by the rectifier 24. Aconstant voltage is generated by utilizing this DC signal by a regulator(not shown) and is supplied to the load 25 such as a battery.

The detecting section 26 is connected to points at both ends of thecapacitor 23 and detects the voltage at these points at both ends of thecapacitor 23 to measure the Q-factor.

[Configuration Example of Detecting Section]

The detecting section 26 has functions to superimpose the Q-factormeasurement signal having a frequency different from that of the powertransmission signal on the power transmission signal received via thepower receiving coil 21 and measure the Q-factor by using the AC signalobtained by removing the power transmission signal from the AC signalresulting from the combining of two signals. In the AC signal obtainedby removing the power transmission signal from the AC signal resultingfrom the combining of these two AC signals, the Q-factor measurementsignal is included.

To realize such a function, the detecting section 26 includes a Q-factormeasurement signal source 31, a resonant frequency adjuster 32, atransmission carrier removing filter portion 33, and a Q-factormeasuring circuit 34 as one example.

The Q-factor measurement signal source 31 has a function similar to thatof the signal source 1 (AC power supply 2) in FIG. 1 and outputs an ACsignal for Q-factor measurement at the time of Q-factor measurement. Thefrequency of the Q-factor measurement signal is set to one differentfrom the frequency (hereinafter, referred to also as the “powertransmission frequency”) of the power transmission signal (powertransmission carrier) transmitted from the power transmission side. Thisallows separation between the power transmission signal and the Q-factormeasurement signal. Thus, power feed and measurement of the Q-factor canbe simultaneously performed.

The resonant frequency adjuster 32 is to change the resonant frequencyof the resonant circuit of the power receiving device 20. As describedabove, the power transmission signal can be separated from the Q-factormeasurement signal by setting the frequency of the power transmissionsignal different from that of the Q-factor measurement signal. However,the capacitors 22 and 23 for resonance, connected to the power receivingcoil 21, are set to such a value that resonance is performed at thepower transmission frequency. Therefore, the resonant frequency adjuster32 for Q-factor measurement for measuring the Q-factor in the resonantstate is used. A capacitor can be applied to the resonant frequencyadjuster 32 as one example. However, it is not limited to this example.For example, it may be configured by using a coil different from thepower receiving coil or by using a coil and a capacitor.

The transmission carrier removing filter portion 33 is inserted betweenthe Q-factor measurement signal source 31 and the resonant frequencyadjuster 32. The purpose of providing the transmission carrier removingfilter portion 33 posterior to (on the downstream side of) the Q-factormeasurement signal source 31 is to prevent the influence of the Q-factormeasurement signal source 31 from being given to the power transmissionsignal (power transmission carrier). Furthermore, the purpose is also toprevent the Q-factor measurement signal source from being broken by thepower transmission signal, in which large amplitude is generated.

Similarly, the transmission carrier removing filter portion 33 is alsoprovided anterior to (on the upstream side of) the Q-factor measuringcircuit 34. This is to remove the power transmission signal from theQ-factor measurement signal superimposed on the power transmissionsignal and measure only the Q-factor measurement signal.

The Q-factor measuring circuit 34 measures the Q-factor by using the ACsignal obtained by removing the power transmission signal from the ACsignal resulting from the combining of two signals, i.e. the powertransmission signal received via the power receiving coil 21 and theQ-factor measurement signal having a frequency different from that ofthe power transmission signal. Then, the detecting section 26 comparesthe Q-factor obtained by the Q-factor measuring circuit 34 with areference value set in advance to thereby determine the state ofelectromagnetic coupling between the power receiving coil 21 and theexternal, specifically e.g. the power transmitting coil 10A of the powertransmitting device 10, i.e. whether or not a metal foreign substancenear the power receiving coil 21 is present.

In this detection processing of a metal foreign substance by theQ-factor measurement, frequency sweep processing to identify theresonant frequency may be executed.

A further description will be made below about the transmission carrierremoving filter portion 33. The transmission carrier removing filterportion 33 is so configured that the seen impedance differs depending onthe seeing direction.

FIG. 3 is a circuit diagram showing part of an internal configurationexample of the transmission carrier removing filter portion 33.

In the example shown in FIG. 3, one terminal of a parallel circuit of acoil L1 and a capacitor C1 is connected to a ground terminal and theother terminal thereof is connected to a terminal 33 a on the side ofthe Q-factor measurement signal source 31. Furthermore, the otherterminal of the parallel circuit of the coil L1 and the capacitor C1 isconnected to one terminal of a parallel circuit of a coil L2 and acapacitor C2. The other terminal of the parallel circuit of the coil L2and the capacitor C2 is connected to a terminal 33 b on the resonantcircuit side, to which the power transmission signal is input.

By this circuit configuration shown in FIG. 3, the Q-factor measurementsignal input from the terminal 33 a on the side of the Q-factormeasurement signal source 31 reaches the terminal 33 b on the resonantcircuit side (passage). On the other hand, the power transmission signalinput from the terminal 33 b on the resonant circuit side does not reachthe terminal 33 a on the side of the Q-factor measurement signal source31 (block). By appropriately selecting the values of the coils L1 and L2and the capacitors C1 and C2, the passage or block can be controlledabout an AC signal having the desired frequency. In the present example,for example, the frequency of the power transmission signal is set to120 kHz and the frequency of the Q-factor measurement signal is set to 2MHz by selecting the values of the coils L1 and L2 and the capacitors C1and C2.

FIG. 4 is a graph showing a frequency characteristic example of theimpedance about the circuit of the transmission carrier removing filterportion 33 shown in FIG. 3.

The example of FIG. 4 represents the impedance of the transmissioncarrier removing filter portion 33 seen from the resonant circuit sideand from the side of the Q-factor measurement signal source 31.

The impedance seen from the resonant circuit side appears high impedanceof 3000 Ω or higher near 120 kHz, which is the power transmissionfrequency (solid characteristic curve). In this case, the Q-factormeasurement signal source 31 appears to have no influence for the powertransmission signal and does not preclude power feed.

On the other hand, when being seen from the Q-factor measurement signalsource 31, the impedance appears low near 2 MHz, which is the frequencyfor Q-factor measurement (dashed characteristic curve). Thus, it ispossible to superimpose the Q-factor measurement signal on the resonantcircuit side.

FIG. 5 shows an example of the relationship between the frequency andfilter passband characteristic of the transmission carrier removingfilter portion 33.

In the example of FIG. 5, loss is large near 120 kHz, which is the powertransmission frequency. Therefore, it turns out that the Q-factormeasurement signal source 31 can be prevented from being broken due toinput of high power of the power transmission signal to the Q-factormeasurement signal source 31.

On the other hand, near 2 MHz as the frequency for Q-factor measurement,the Q-factor measurement signal has smaller loss compared with 120 kHzas the power transmission frequency and thus passes. Therefore, it canbe superimposed on the power transmission signal. Loss L of the Q-factormeasurement signal near 2 MHz is about 18 dB. However, this level ofloss causes no problem because about 50 mV is enough as the amplitude ofthe voltage input to the resonant circuit including the power receivingcoil 21.

In this manner, the transmission carrier removing filter portion 33 ofthe detecting section 26 (FIG. 2) allows the passage of the Q-factormeasurement signal generated by the Q-factor measurement signal source31 and does not allow the passage of the power transmission signal inthe direction from the resonant circuit side (including the resonantfrequency adjuster 32) toward the Q-factor measurement signal source 31and the Q-factor measuring circuit 34.

FIG. 6 shows the state in which actually the power transmission signalof 120 kHz and the Q-factor measurement signal of 2 MHz aresuperimposed. FIG. 6 is a graph showing a waveform example of a voltageV1 and a voltage V2 in FIG. 2.

From FIG. 6, it turns out that the Q-factor measurement signal (voltageV2) of 2 MHz is amplified across the capacitor 23. When actually thesignals are separated by frequency and the amplitude of the Q-factormeasurement signal is seen, it can be confirmed that the voltage V2(upper side in FIG. 6) on the posterior side of the capacitor 23 (on theside of the rectifier 24) is Q times the voltage V1 (lower side in FIG.6) on the anterior side of the capacitor 23 (on the side of the powerreceiving coil 21).

FIGS. 7A and 7B are graphs showing a spectrum characteristic example ofthe respective voltages. FIG. 7A shows the spectrum characteristic ofthe voltage V1 and FIG. 7B shows the spectrum characteristic of thevoltage V2.

As shown in FIGS. 7A and 7B, when the respective voltages are seen onthe frequency axis, the Q-factor measurement signal of 2 MHz isamplified from 16 mV to 220 mV and is calculated as about 14 when beingconverted to the Q-factor. On the other hand, about the power receivingcoil 21, the measurement result when the Q-factor in the Q-factormeasurement state is seen by an LCR meter is shown in FIG. 8. In theexample of FIG. 8, the Q-factor is 15 to 16 near 2 MHz. Thus, it can beconfirmed that the Q-factor can be measured with high accuracy.

As described above, according to the first embodiment, the resonantfrequency adjuster 32 of the detecting section 26 is provided and theconfiguration is so made that the resonant circuit resonates at a newfrequency (second frequency) different from the resonant frequency(first frequency) of the resonant circuit composed of the powerreceiving coil 21 and the capacitors 22 and 23.

Furthermore, by the transmission carrier removing filter portion 33 ofthe detecting section 26, the Q-factor measurement signal having afrequency different from that of the power transmission signal issuperimposed on the power transmission signal received via the powerreceiving coil 21 and the Q-factor is measured by using the AC signalobtained by removing the power transmission signal from the AC signalresulting from the combining of two signals.

Therefore, the power receiving device can perform the Q-factormeasurement while receiving the power transmission signal from the powertransmitting device. Because operation of stopping the powertransmission is absent, the communication between the transmission andreception sides can be reduced and simplification of the control flow isexpected.

Furthermore, a new coil and sensor do not need to be added.

In addition, it is possible to detect a metal foreign substance withhigh accuracy compared with the related-art method for foreign substancedetection and so forth based on the DC-DC efficiency.

Moreover, because the control flow is simplified, the redundant timenecessary for the control for the Q-factor measurement is reduced andthe power transmission efficiency per unit time is enhanced. Or theoperation of detecting a metal foreign substance can be carried out at ashorter interval, which leads to early detection of a metal foreignsubstance.

Furthermore, when the number of power receiving devices is two or more,power transmission to the power receiving devices other than the powerreceiving device in which Q-factor measurement is being performed doesnot need to be stopped. Therefore, power transmission, Q-factormeasurement, and so forth can be performed in parallel in each of theplural power receiving devices.

(Other Configuration Examples of Resonant Circuit)

In the above-described first embodiment, the example is explained inwhich the capacitor 22 in parallel to the power receiving coil 21 andthe capacitor 23 in series to the parallel connection of the powerreceiving coil 21 and the capacitor 22 are used for impedance matchingof the power receiving coil 21 of the resonant circuit in the state inwhich the resonant frequency adjuster 32 is not connected thereto.However, another configuration can be employed as the resonant circuit.

FIG. 9A to FIG. 9C are circuit diagrams showing other configurationexamples of the resonant circuit.

FIG. 9A shows an example in which the resonant circuit in the state inwhich the resonant frequency adjuster 32 is not connected thereto isconfigured by using the capacitor 22 in parallel to the power receivingcoil 21. The resonant frequency adjuster 32 is connected to theconnecting point between the power receiving coil 21 and the capacitor22 configuring this resonant circuit.

FIG. 9B shows an example in which the resonant circuit in the state inwhich the resonant frequency adjuster 32 is not connected thereto isconfigured by using a capacitor 23A in series to the power receivingcoil 21. The resonant frequency adjuster 32 is connected to therectifier side of the capacitor 23A configuring this resonant circuit.

FIG. 9C shows an example in which the resonant circuit in the state inwhich the resonant frequency adjuster 32 is not connected thereto isconfigured by using the power receiving coil 21, the capacitor 23A, anda capacitor 22A to form a closed circuit. The resonant frequencyadjuster 32 is connected to the connecting middle point between thecapacitor 23A and the capacitor 22A configuring this resonant circuit.

In all resonant circuits, the voltage V2 between both ends of the powerreceiving coil 21 and the voltage V1 from the power receiving coil 21 tothe resonant frequency adjuster 32 are detected to measure the Q-factor.

These resonant circuits are one example and the configuration of theresonant circuit is not limited to these examples.

[Modification Example of First Embodiment]

As a modification example of the first embodiment, an example in whichthe connecting point of the resonant frequency adjuster 32 of the powerreceiving device is changed will be described.

FIG. 10 is a schematic circuit diagram showing a configuration exampleof the power receiving device in the contactless power transmissionsystem according to the modification example (hereinafter, referred toalso as the “present example”) of the first embodiment of the presentdisclosure. In the description of FIG. 10, explanation is omitted aboutthe same configuration as that in FIG. 2.

A contactless power transmission system 100A shown in FIG. 10 includesthe power transmitting device 10 (primary side) including at least thepower transmitting coil 10A and a power receiving device 20A (secondaryside). The power receiving device 20A is one example of the detectingdevice.

The power receiving device 20A of the present example is different fromthe power receiving device 20 of FIG. 2 in the connection between theresonant circuit and the resonant frequency adjuster 32.

In the power receiving device 20, the resonant frequency adjuster 32 isconnected to the connecting middle point between the capacitor 23 andthe rectifier 24. In the power receiving device 20A of the presentexample, the resonant frequency adjuster 32 is connected to theconnecting middle point between the parallel connection of the coil 21and the capacitor 22 and a capacitor 23′. The capacitor 23′ is alsoconnected to the rectifier 24. The capacitor 23′ of the power receivingdevice 20A corresponds to the capacitor 23 of the power receiving device20 and configures a resonant circuit.

The resonant frequency adjuster 32 of the power receiving device 20A isto measure the Q-factor in the resonant state and changes the resonantfrequency of the resonant circuit of the power receiving device 20Asimilarly to the power receiving device 20.

Also in the power receiving device 20A configured in this manner, thevoltage V1 and the voltage V2 of the Q-factor measurement signal can bemeasured and the Q-factor of the power receiving coil 21 can be measuredsimilarly.

Compared with FIG. 2, in the configuration of FIG. 10, the resonantfrequency of the Q-factor measurement signal can be set lower than thefrequency of the power transmission signal even when the resonantfrequency adjuster 32 is configured by only a capacitor. In this case,the Q-factor measurement can be performed with the Q-factor measurementsignal having a frequency lower than that of the power transmissionsignal and the influence of that harmonic components and so forth of thepower transmission signal look noise against the Q-factor measurementsignal can be alleviated.

(Other Configuration Examples of Resonant Circuit)

In the above-described modification example of the first embodiment, theexample is explained in which the capacitor 22 in parallel to the powerreceiving coil 21 and the capacitor 23′ in series to the parallelconnection of the power receiving coil 21 and the capacitor 22 are usedfor impedance matching of the power receiving coil 21 of the resonantcircuit in the state in which the resonant frequency adjuster 32 is notconnected thereto. However, another configuration can be employed as theresonant circuit.

FIG. 11A and FIG. 11B are circuit diagrams showing other configurationexamples of the resonant circuit.

FIG. 11A shows an example in which the resonant circuit in the state inwhich the resonant frequency adjuster 32 is not connected thereto isconfigured by using a capacitor 23A′ in series to the power receivingcoil 21. The resonant frequency adjuster 32 is connected to theconnecting middle point between the power receiving coil 21 and thecapacitor 23A′ configuring this resonant circuit.

FIG. 11B shows an example in which the resonant circuit in the state inwhich the resonant frequency adjuster 32 is not connected thereto isconfigured by using the power receiving coil 21, the capacitor 23A′, anda capacitor 22A′ to form a closed circuit. The resonant frequencyadjuster 32 is connected to the connecting middle point between thepower receiving coil 21 and the capacitor 23A′ configuring this resonantcircuit.

In all resonant circuits, the voltage V2 between both ends of the powerreceiving coil 21 and the voltage V1 from the power receiving coil 21 tothe resonant frequency adjuster 32 are detected to measure the Q-factor.

These resonant circuits are one example and the configuration of theresonant circuit is not limited to these examples.

3. Second Embodiment

To accurately measure the Q-factor of the resonant circuit, theimpedance of the rectifier side from the viewpoint of the resonantcircuit should be high. For this purpose, the rectifier may be separatedto be set to the open state as one example.

So, in a second embodiment, an example will be explained in which aseparator to separate the load is provided for the power receivingdevice 20 (see FIG. 2) according to the first embodiment so that thedetecting section may be separated from the load in Q-factormeasurement.

Power cannot be received when the rectifier is separated. However, evenin this case, there is an advantage that the system does not need to gothrough a complicated control flow of stopping power transmission of theprimary side. The power supply to the Q-factor measuring circuit in thiscase is driven by using the load 25 (battery etc.) possessed on thesecondary side or a charge stored in the capacitor.

[Configuration Example of Power Receiving Device]

FIG. 12 is a circuit diagram showing a configuration example of a powerreceiving device according to the second embodiment of the presentdisclosure. In the following, the differences between a power receivingdevice 40 shown in FIG. 12 and the power receiving device 20 accordingto the first embodiment will be mainly explained and explanation of theother part will be omitted.

The power receiving device 40 according to the present embodiment isdifferent from the power receiving device 20 of FIG. 2 mainly in that acommunication section 41 for transmitting data to the external, acapacitor 42 for the charge, and a separator 44 are provided.

The communication section 41 is formed of a series circuit of aresistive element 41R and a switch part 41S and is connected in parallelbetween the resonant circuit and the rectifier 24. Specifically, oneterminal of the series circuit of the resistive element 41R and theswitch part 41S is connected to the capacitor 23 and the other terminalis connected to the power receiving coil 21 and the capacitor 22.

When data transmission is performed from the power receiving device 20to the power transmitting device 10, it can be performed by using e.g. aload modulation system. Specifically, the value of the load resistivecomponent in parallel to the power receiving coil 21 is changed throughswitching of opening/closing of the switch part 41S by a control section46 in association with a transmission data string (baseband signal).Thereby, the AC signal output by the power transmitting device 10 issubjected to amplitude modulation and the transmission data string fromthe power receiving device 20 is observed on the side of the powertransmitting device 10.

Although the example in which communication is performed by utilizing aload modulation system is explained in this example, anothershort-distance wireless communication system such as Bluetooth(registered trademark) or ZigBee (registered trademark) may be utilized.

On the subsequent stage side of the rectifier 24, the capacitor 42 and aswitch part 43 are connected in series. One terminal of this capacitor42 is connected to one output terminal of the rectifier 24 and oneterminal of the switch part 43 is connected to the other output terminalof the rectifier 24. Furthermore, one and the other output terminals ofthe rectifier 24 are connected to one and the other input terminals of aregulator 27. One and the other output terminals of the regulator 27 areconnected to a load.

The regulator 27 carries out control so that the output voltage andcurrent may be always kept constant. As one example, it supplies aconstant voltage signal (power supply) to the power feed target (load)and the respective blocks typified by the detecting section 26. Aregulator different from the regulator 27 may be provided to separatethe constant voltage signal supplied to the power feed target from thatsupplied to the respective blocks.

The separator 44 is provided between the communication section 41 andthe rectifier 24 as one example. Under control by the control section46, it is turned on in power feed to supply power to the load whereas itis turned off in Q-factor measurement to separate the load. The positionat which the separator 44 is disposed is not limited thereto. Forexample, the following positions will be available: inside of therectifier 24, position between the rectifier 24 and the capacitor 42 forthe charge, and position anterior or posterior to the regulator 27.

As one example, a switching element such as a transistor or a MOSFET canbe applied to the switch parts 41S and 43 and the separator 44.

A determining section 45 is connected to the Q-factor measuring circuit34 of the detecting section 26 and compares the Q-factor input from theQ-factor measuring circuit 34 with a reference value stored in anon-volatile memory 47. Then, the determining section 45 determineswhether or not a metal foreign substance exists near the power receivingcoil 21 based on the result of the comparison and outputs thedetermination result to the control section 46.

The control section 46 is one example of the control section. Itcontrols the communication section 41 according to need and transmitsthe determination result of the metal foreign substance from the powerreceiving coil 21 to the power transmitting device 10. Moreover, thecontrol section 46 switches On/Off of the switch part 43 and carries outcontrol to charge the capacitor 42 for the charge with a DC signalsupplied from the rectifier 24. An arithmetic processing device such asa micro-processing unit (MPU) can be applied to the control section 46.

The processing of the determining section 45 and the control section 46may be handled by one MPU. Alternatively, a configuration may beemployed in which the processing of the determining section 45, thecontrol section 46, and the Q-factor measuring circuit 34 or theprocessing of the determining section 45, the control section 46, theQ-factor measuring circuit 34, and the transmission carrier removingfilter portion 33 is handled by an analog-digital converter and an MPU.

The memory 47 stores the reference values of the secondary-side Q-factoron a frequency-by-frequency basis, measured in advance in the state inwhich no object exists near the power receiving coil 21 or no object isput on the power receiving coil 21. Furthermore, the memory 47 may storean ID number (identification information) allocated to each powerreceiving device, an ID number acquired from the power transmittingdevice, and so forth.

In the power receiving device 40 shown in FIG. 12, the connection formshown in FIG. 2 is employed as the connection form between the resonantcircuit and the resonant frequency adjuster 32. However, it is obviousthat the connection form shown in FIG. 10 may be employed. Furthermore,the resonant circuit of the power receiving device 40 can employ variousconfigurations of the resonant circuit like those shown in FIGS. 9A to9C and FIGS. 11A and 11B.

[Operation Example of Power Receiving Device] First Example

An operation example of the power receiving device 40 will be described.FIG. 13 is a flowchart showing an operation example (first example) inQ-factor measurement of the contactless power transmission systemincluding the power transmitting device 10 (FIG. 2) and the powerreceiving device 40.

First, the power transmitting device 10 (primary side) starts powertransmission (step S1) and continues the power transmission until anorder of power transmission stop or the like is issued (step S2).

On the other hand, the power receiving device 40 (secondary side)receives the power transmission signal output from the powertransmitting device 10 and starts power reception (step S3). Thereupon,the control section 46 controls the communication section 41 to transmita power reception confirmation signal to the power transmitting device10 (step S4). The power reception confirmation signal is output to thepower transmitting device by the power receiving device that iscurrently receiving power and includes information indicating that itsoutput source is currently receiving power. In the processing of thesesteps S3 and S4, the power receiving device 40 operates by using thepower of the power transmission signal received from the primary side.

The power transmitting device 10 determines whether or not the powerreception confirmation signal is received from the power receivingdevice 40 (step S5). If the power reception confirmation signal is notreceived, the power transmitting device 10 stops the power transmissionand executes end processing (step S6). If the power receptionconfirmation signal is received, the power transmitting device 10 movesto the processing of the step S2 to continue the power transmission.

After transmitting the power reception confirmation signal, the controlsection 46 of the power receiving device 40 turns on the switch part 43to obtain from the power transmission signal the power consumed in thedetecting section 26 and so forth at least in Q-factor measurement andcharge the capacitor 42 for the charge with the obtained power (stepS7). After charging the capacitor 42 with the power necessary forQ-factor measurement, the control section 46 turns off the separator 44to separate the load (step S8).

The respective portions in the detecting section 26 perform Q-factormeasurement after the load is separated from the detecting section 26.First, the Q-factor measurement signal source 31 generates the Q-factormeasurement signal having a frequency different from that of the powertransmission signal received by the power receiving coil 21 (step S9).

The Q-factor measurement signal generated by the Q-factor measurementsignal source 31 passes through the transmission carrier removing filterportion 33 to be superimposed on the power transmission signal. Then,the power transmission signal is removed by the transmission carrierremoving filter portion 33 from the AC signal resulting from thecombining of the power transmission signal and the Q-factor measurementsignal, and this AC signal from which the power transmission signal isremoved, i.e. the Q-factor measurement signal (voltages V1 and V2), isinput to the Q-factor measuring circuit 34.

The Q-factor measuring circuit 34 detects, from the input Q-factormeasurement signal, the voltage V1 between the resonant frequencyadjuster 32 and the transmission carrier removing filter portion 33 andthe voltage V2 on the anterior side of the capacitor 23. Then, theQ-factor measuring circuit 34 records the voltages V1 and V2 in e.g. thememory 47 and calculates the Q-factor (step S10).

The determining section 45 compares the Q-factor calculated by theQ-factor measuring circuit 34 with the reference value retained in thememory 47 and determines whether or not a metal foreign substance existsnear the power receiving coil 21 (step S11).

If the determining section 45 determines that a metal foreign substanceis absent, the control section 46 turns on the separator 44 to connectthe resonant circuit and the detecting section 26 to the load (step S12)and moves to the processing of transmitting the power receptionconfirmation signal in the step S4.

If it is determined that a metal foreign substance is present, thecontrol section 46 executes power reception end processing (step S13).

In the processing of these steps S7 to S13, the power receiving device40 operates by utilizing the power stored in the secondary-side batteryor the capacitor. In this example, the power receiving device 40utilizes the power stored in the capacitor 42.

As just described, the configuration is so made that the separator 44 isturned on in power feed to supply power to the load whereas theseparator 44 is turned off in Q-factor measurement to separate the load.Therefore, the accurate Q-factor measurement can be performed withoutsuffering from the influence of the load side in the Q-factormeasurement.

Second Example

FIG. 14 is a flowchart showing an operation example (second example) inQ-factor measurement of the contactless power transmission systemincluding the power transmitting device 10 (FIG. 2) and the powerreceiving device 40. The second example is different from the firstexample in that the determination result of the metal foreign substanceis transmitted from the power receiving device 40 to the powertransmitting device 10.

Processing of steps S41 to S52 in FIG. 14 is the same as the processingof the steps S1 to S12 in FIG. 13 and therefore description thereof isomitted.

If it is determined in determination processing of the step S51 that ametal foreign substance is present, the control section 46 controls thecommunication section 41 to transmit a foreign substance detectionsignal to the power transmitting device 10 (step S53). Then, aftertransmitting the foreign substance detection signal to the powertransmitting device 10, the control section 46 executes power receptionend processing (step S54).

The power transmitting device 10 determines whether or not the foreignsubstance detection signal is received from the power receiving device40 (step S55). If the foreign substance detection signal is notreceived, the power transmitting device 10 moves to the processing ofthe step S42 to continue the power transmission. If the foreignsubstance detection signal is received, the power transmitting device 10stops the power transmission and executes abnormal end processing (stepS56).

In this manner, when determining that a metal foreign substance ispresent, the power receiving device 40 transmits the foreign substancedetection signal to the power transmitting device 10. Thereby, even whenthe power reception confirmation signal is not transmitted from thepower receiving device 40, the power transmitting device 10 canunderstand the reason for this. For example, when getting to know theexistence of a metal foreign substance between the power transmittingdevice 10 and the power receiving device 40, the power transmittingdevice 10 can take a proper countermeasure against heat generation ofthe metal foreign substance, such as stopping the power transmission ormaking abnormal end.

4. Third Embodiment [Configuration Example of Power Receiving Device]

For example, when a filter section is disposed anterior to (on theresonant circuit side of) the rectifier 24 in FIG. 2, Q-factormeasurement can be performed without stopping power reception althoughthere is a possibility of increase in loss of the power transmissionsignal.

So, in a third embodiment, an example will be explained in which ameasurement signal removing filter section 56 is provided anterior to(on the resonant circuit side of) the rectifier 24 of the powerreceiving device 20 (see FIG. 2) according to the first embodiment. Thisconfiguration allows the impedance of the rectifier side to appear highfor the Q-factor measurement signal.

FIG. 15 is a circuit diagram showing a configuration example of a powerreceiving device according to the third embodiment of the presentdisclosure.

In a power receiving device 50, the measurement signal removing filtersection 56 is provided between the capacitor 23 and the rectifier 24. Incontrast to the transmission carrier removing filter portion 33, themeasurement signal removing filter section 56 allows the passage of thepower transmission signal with the first frequency received by the powerreceiving coil 21 and blocks the Q-factor measurement signal with thesecond frequency generated by the Q-factor measurement signal source 31.

In the example of FIG. 15, as one example, a detecting section 26Aincludes amplifiers 52A and 52B, transmission carrier removing filterportions 33A and 33B at the subsequent stage thereof, rectifiers 53A and53B, an analog-digital converter (hereinafter, referred to as the “ADC”)54, an arithmetic processor 55, and a capacitor 32A. Furthermore, thedetecting section 26A includes the Q-factor measurement signal source31, an amplifier 51, and a transmission carrier removing filter portion33C. The transmission carrier removing filter portions 33A to 33Ccorrespond to the transmission carrier removing filter portion 33.

In addition, the power receiving device 50 includes the determiningsection 45 connected to the arithmetic processor 55 of the detectingsection 26A, the control section 46 connected to this determiningsection 45, and the memory 47 connected to the determining section 45and the control section 46.

The capacitor 32A is one example of the resonant frequency adjuster 32(see FIG. 2). One terminal thereof is connected to the connecting middlepoint between the capacitor 23 and the measurement signal removingfilter section 56. The other terminal of the capacitor 32A is connectedto the transmission carrier removing filter portion 33C.

The input terminal of the amplifier 52A is connected to the otherterminal of the capacitor 32A for resonant frequency adjustment. Theinput terminal of the amplifier 52B is connected to the connectingmiddle point between the capacitor 22 and the capacitor 23.

The output terminal of the amplifier 52A is connected to thetransmission carrier removing filter portion 33A and the output terminalof the amplifier 52B is connected to the transmission carrier removingfilter portion 33B. The transmission carrier removing filter portions33A and 33B remove the power transmission signal from the AC signalresulting from combining of the input power transmission signal andQ-factor measurement signal. Then, the transmission carrier removingfilter portion 33A inputs the AC signal (corresponding to the voltageV1) resulting from the removal of the power transmission signal to therectifier 53A. Furthermore, the transmission carrier removing filterportion 33B inputs the AC signal (corresponding to the voltage V2)resulting from the removal of the power transmission signal to therectifier 53B.

The rectifier 53A detects (rectifies) the input AC signal and inputs thedetected signal to the ADC 54 and the rectifier 53B detects (rectifies)the input AC signal and inputs the detected signal to the ADC 54.

The ADC 54 converts the analog detected signals input from therectifiers 53A and 53B to digital signals and outputs the respectivesignals to the arithmetic processor 55.

As one example of the Q-factor measuring circuit 34 in FIG. 2, thearithmetic processor 55 calculates the ratio between the voltage V1 andthe voltage V2, i.e. the Q-factor, from the detected signals input fromthe ADC 54 and outputs this Q-factor to the determining section 45. Forexample, an arithmetic processing device such as a micro-processing unit(MPU) can be applied to the arithmetic processor 55.

Then, the determining section 45 compares the Q-factor calculated by thearithmetic processor 55 with the reference value retained in the memory47 and determines whether or not a metal foreign substance is present.The determining section 45 outputs the determination result to thecontrol section 46.

Although the communication section 41 like that in the power receivingdevice 40 of FIG. 12 is not shown in the power receiving device 50 shownin FIG. 15, the power receiving device 50 also includes thecommunication section 41.

In the configuration shown in FIG. 15, by providing the transmissioncarrier removing filter portions 33A to 33C and the measurement signalremoving filter section 56, an equivalent circuit 50A shown in FIG. 16is realized for the power transmission frequency and an equivalentcircuit 50B shown in FIG. 17 is realized for the Q-factor measurementfrequency.

Specifically, for the power transmission frequency, a circuit equivalentto the state in which the detecting section 26A does not exist isobtained as shown in FIG. 16. For the Q-factor measurement frequency, asshown in FIG. 17, a circuit equivalent to the state in which theconfiguration of the detecting section 26A changes as if it becomes theconfiguration of a detecting section 26A′ and the load subsequent to therectifier 24 is not connected is obtained.

In the power receiving device 50 shown in FIG. 15, the connection formshown in FIG. 2 is employed as the connection form between the resonantcircuit and the resonant frequency adjuster 32. However, it is obviousthat the connection form shown in FIG. 10 may be employed. Furthermore,the resonant circuit of the power receiving device 50 can employ variousconfigurations of the resonant circuit like those shown in FIGS. 9A to9C and FIGS. 11A and 11B.

[Operation Example of Power Receiving Device] First Example

An operation example of the power receiving device 50 will be described.FIG. 18 is a flowchart showing an operation example (first example) inQ-factor measurement of a contactless power transmission systemincluding the power transmitting device 10 (FIG. 2) and the powerreceiving device 50. In this example, the processing of capacitor chargeand load separation is unnecessary compared with the flowchart of FIG.13.

Processing from steps S21 to S26, in which first the power transmittingdevice 10 (primary side) starts power transmission and then the powerreceiving device 50 starts power reception and transmits the powerreception confirmation signal to the power transmitting device 10 andthereafter the power transmitting device 10 reacts depending on whetheror not this power reception confirmation signal is received, is the sameas the processing from the steps S1 to S6 in FIG. 13 and thereforedescription thereof is omitted.

After the end of the processing of the step S24, the respective sectionsin the detecting section 26A perform Q-factor measurement. First, theQ-factor measurement signal source 31 generates the Q-factor measurementsignal having a frequency different from that of the power transmissionsignal received by the power receiving coil 21 (step S27).

The Q-factor measurement signal generated by the Q-factor measurementsignal source 31 passes through the transmission carrier removing filterportion 33C to be superimposed on the power transmission signal. Then,the power transmission signal is removed by the transmission carrierremoving filter portions 33A and 33B from the AC signal obtained by thecombining of the power transmission signal and the Q-factor measurementsignal. This AC signal from which the power transmission signal isremoved, i.e. the Q-factor measurement signal (voltages V1 and V2), isinput to the rectifiers 53A and 53B to be supplied to the arithmeticprocessor 55 finally.

The arithmetic processor 55 detects, from the input Q-factor measurementsignal, the voltage V1 applied to the whole of the power receiving coil21 and the capacitors 23 and 32A and the voltage V2 on the anterior sideof the capacitor 23. Then, the arithmetic processor 55 records thevoltages V1 and V2 in e.g. the memory 47 and calculates the Q-factor(step S28).

The determining section 45 compares the Q-factor calculated by thearithmetic processor 55 with the reference value retained in the memory47 and determines whether or not a metal foreign substance exists nearthe power receiving coil 21 (step S29).

If the determining section 45 determines that a metal foreign substanceis absent, the control section 46 moves to the processing oftransmitting the power reception confirmation signal in the step S24.

If it is determined that a metal foreign substance is present, thecontrol section 46 executes power reception end processing (step S30).

In this manner, without separating the load by the separator, accurateQ-factor measurement can be performed by the transmission carrierremoving filter portion and the measurement signal removing filtersection. Furthermore, because the load separation is not performed, thepower transmission signal of the primary side can be utilized as thepower supply of the power receiving device 50. Therefore, the powerreceiving device 50 can carry out the series of operation by using thepower of the power transmission signal received from the primary sidewithout using a battery or a capacitor.

Second Example

FIG. 19 is a flowchart showing an operation example (second example) inQ-factor measurement of the contactless power transmission systemincluding the power transmitting device 10 (FIG. 2) and the powerreceiving device 50. The second example is different from the firstexample in that the determination result of the metal foreign substanceis transmitted from the power receiving device 50 to the powertransmitting device 10.

Processing of steps S61 to S69 in FIG. 19 is the same as the processingof the steps S21 to S29 in FIG. 18 and therefore description thereof isomitted.

If it is determined in determination processing of the step S69 that ametal foreign substance is present, the control section 46 controls thecommunication section 41 to transmit the foreign substance detectionsignal to the power transmitting device 10 (step S70). Then, aftertransmitting the foreign substance detection signal to the powertransmitting device 10, the control section 46 executes power receptionend processing (step S71).

The power transmitting device 10 determines whether or not the foreignsubstance detection signal is received from the power receiving device50 (step S72). If the foreign substance detection signal is notreceived, the power transmitting device 10 moves to the processing ofthe step S62 to continue the power transmission. If the foreignsubstance detection signal is received, the power transmitting device 10stops the power transmission and executes abnormal end processing (stepS73).

In this manner, when determining that a metal foreign substance ispresent, the power receiving device 50 transmits the foreign substancedetection signal to the power transmitting device 10. Thereby, even whenthe power reception confirmation signal is not transmitted from thepower receiving device 50, the power transmitting device 10 canunderstand the reason for this. For example, when getting to know theexistence of a metal foreign substance between the power transmittingdevice 10 and the power receiving device 50, the power transmittingdevice 10 can take a proper countermeasure against heat generation ofthe metal foreign substance, such as stopping the power transmission ormaking abnormal end.

5. Others

In the above-described first to third embodiment examples, the detectingsections 26 and 26A of the power receiving devices 20, 20A, 40, and 50obtain the Q-factor from the voltage V1 between both ends of the coil ofthe resonant circuit and the resonant frequency adjuster 32 (capacitor,as one example) and the voltage V2 between both ends of the powerreceiving coil 21. However, the Q-factor may be obtained by a half widthmethod.

In the half width method, when a series resonant circuit is configured,the Q-factor is obtained by the following expression (2) based on theband (frequency f1 to f2) corresponding to the impedance that is √2times the absolute value of the impedance (Zpeak) at a resonantfrequency f0 as shown in a graph of FIG. 20.

Error! Objects cannot be created from editing field codes.

When a parallel resonant circuit is configured, the Q-factor is obtainedby expression (2) based on the band (frequency f1 to f2) correspondingto the impedance that is 1/√2 times the absolute value of the impedance(Zpeak) at the resonant frequency f0 as shown in a graph of FIG. 21.

In the above-described embodiment examples, Q-factor measurement andprocessing of detecting a metal foreign substance are executed in thepower receiving device. However, the configuration is not limited tothese examples. It is also possible to employ the followingconfiguration. Specifically, information on the voltages V1 and V2measured in the power receiving devices 20, 20A, 40, and 50, thefrequency of the Q-factor measurement signal at the time of measurement,and the Q-factor reference value at this frequency are transmitted tothe power transmitting device 10. Then, calculation of thesecondary-side Q-factor and determination as to whether or not a metalforeign substance is present are performed in e.g. the determiningsection 45 of the power transmitting device 10. In this case, theprocessing burden of the power receiving device is reduced.

In the above-described embodiment examples, the explanation is madebased on the assumption that the contactless power transmission systemof the magnetic resonance system is configured. However, as alreadydescribed, embodiments of the present disclosure are not limited to themagnetic resonance system and can be applied also to the electromagneticinduction system, in which the coupling coefficient k is set high andthe Q-factor is set low.

In the above-described embodiment examples, the power transmittingdevice 10 is explained as the configuration having only the powertransmission function and the power receiving devices 20, 20A, 40, and50 are explained as the configuration having only the power receptionfunction. However, the configuration is not limited thereto. Forexample, the power transmitting device 10 may have the power receptionfunction and be capable of receiving power from the external via thepower transmitting coil 10A. Conversely, the power receiving device 20may have the power transmission function and be capable of transmittingpower to the external via the power receiving coil 21.

In the above-described embodiment examples, the Q-factor at the resonantfrequency is measured. However, the frequency at which the Q-factor ismeasured does not necessarily need to correspond with the resonantfrequency. Even when the Q-factor is measured by using a frequencyshifted from the resonant frequency within the allowable range, it ispossible to enhance the accuracy of detection of the metal foreignsubstance existing between the power transmission side and the powerreception side by utilizing the technique of the embodiments of thepresent disclosure.

Due to the approach of a conductor such as a metal to the powertransmitting coil or the power receiving coil, not only the Q-factor butalso the L value changes, so that the resonant frequency is shifted. Thestate of electromagnetic coupling may be detected by using both theamount of shift of the resonant frequency due to the change in the Lvalue and the Q-factor in combination.

When a metal foreign substance is sandwiched between the powertransmitting coil and the power receiving coil, the value of thecoupling coefficient k also changes. The changes in both the value ofthe coupling coefficient k and the Q-factor may be used in combinationfor detection of the state of electromagnetic coupling.

In the above-described embodiment examples, examples of a coil having nocore are explained as the power transmitting coil and the powerreceiving coil. However, a coil having such a structure as to be woundaround a core having a magnetic body may be employed.

In the embodiment examples of the present disclosure, the portableapparatus of the secondary side can be applied to various pieces ofapparatus requiring power, such as cellular phone, portable musicplayer, and digital still camera.

The present disclosure can take also the following configurations.

(1)

A detecting device including:

a coil configured to be electromagnetically coupled to an external;

a resonant circuit configured to include at least the coil; and

a detecting section configured to superimpose a measurement signal formeasuring a Q-factor of the resonant circuit on a power transmissionsignal transmitted to the coil in a contactless manner and remove thepower transmission signal from an alternating-current signal obtained bysuperimposing the measurement signal on the power transmission signal,the detecting section measuring the Q-factor by using thealternating-current signal from which the power transmission signal isremoved.

(2)

The detecting device according to the above-described (1), wherein

the power transmission signal is an alternating-current signal with afirst frequency and the measurement signal is an alternating-currentsignal with a second frequency different from the first frequency.

(3)

The detecting device according to the above-described (1) or (2),wherein

the detecting section includes

-   -   a resonant frequency adjuster that is connected to the resonant        circuit and is to change resonant frequency of the resonant        circuit from the first frequency to the second frequency,    -   a first frequency remover that does not allow passage of the        alternating-current signal with the first frequency and allows        passage of at least the alternating-current signal with the        second frequency, and    -   a Q-factor measuring section that calculates the Q-factor by        using the alternating-current signal that has passed through the        first frequency remover and includes the measurement signal.        (4)

The detecting device according to any of the above-described (1) to (3),further including

a separator configured to be connected to a side to which a load on anopposite side to at least the coil across the resonant circuit isconnected, and electrically separate the load from the resonant circuitwhen the detecting section measures the Q-factor.

(5)

The detecting device according to any of the above-described (1) to (4),further including

a power storage configured to be charged with at least power consumed inmeasurement of the Q-factor in the detecting section by using the powertransmission signal received by the coil from the external,

wherein the detecting section measures the Q-factor by using the powerstored in the power storage in a period when connection between theresonant circuit and the load is set off.

(6)

The detecting device according to any of the above-described (3) to (5),further including

a second frequency remover configured to be connected to a side to whicha load on an opposite side to at least the coil across the resonantcircuit is connected, and allow passage of the alternating-currentsignal with the first frequency, the second frequency remover notallowing passage of at least the alternating-current signal with thesecond frequency.

(7)

The detecting device according to any of the above-described (3) to (6),wherein

the resonant frequency adjuster includes at least either a capacitor ora coil and is connected between the resonant circuit and the firstfrequency remover.

(8)

The detecting device according to any of the above-described (3) to (7),further including

a determining section configured to compare the Q-factor obtained by theQ-factor measuring section with a reference value set in advance todetermine a state of electromagnetic coupling between the coil and theexternal.

(9)

The detecting device according to the above-described (8), wherein

the state of electromagnetic coupling between the coil and the externalis whether or not a conductor near the coil or a circuit including anycoil exists.

(10)

The detecting device according to any of the above-described (3) to (9),wherein

the Q-factor measuring section acquires a first voltage applied betweenboth ends of the coil configuring the resonant circuit and the resonantfrequency adjuster and a second voltage applied between both ends of thecoil from the alternating-current signal that has passed through thefirst frequency remover, and calculates the Q-factor from a ratiobetween the first voltage and the second voltage.

(11)

The detecting device according to any of the above-described (3) to(10), wherein

the Q-factor measuring section calculates the Q-factor by using a halfwidth method in which the Q-factor is obtained from a band correspondingto √2 times an absolute value of impedance of a series resonant circuitincluding at least the coil at resonant frequency.

(12)

The detecting device according to any of the above-described (3) to(11), wherein

the Q-factor measuring section calculates the Q-factor by using a halfwidth method in which the Q-factor is obtained from a band correspondingto 1/√2 times an absolute value of impedance of a parallel resonantcircuit including at least the coil at resonant frequency.

(13)

The detecting device according to any of the above-described (3) to(11), further including a communication section configured to transmitthe Q-factor measured by the detecting section to a power transmissionside of the power transmission signal.

(14)

A power receiving device including:

a coil configured to be used to receive power from an external;

a resonant circuit configured to include at least the coil; and

a detecting section configured to superimpose a measurement signal formeasuring a Q-factor of the resonant circuit on a power transmissionsignal transmitted to the coil in a contactless manner and remove thepower transmission signal from an alternating-current signal obtained bysuperimposing the measurement signal on the power transmission signal,the detecting section measuring the Q-factor by using thealternating-current signal from which the power transmission signal isremoved.

(15)

The power receiving device according to the above-described (14),wherein

the detecting section includes

-   -   a resonant frequency adjuster that is connected to the resonant        circuit and is to change resonant frequency of the resonant        circuit from a first frequency to a second frequency different        from the first frequency,    -   a first frequency remover that does not allow passage of an        alternating-current signal with the first frequency and allows        passage of at least an alternating-current signal with the        second frequency, and    -   a Q-factor measuring section that calculates the Q-factor by        using the alternating-current signal that has passed through the        first frequency remover and includes the measurement signal.        (16)

A contactless power transmission system including:

a power transmitting device that wirelessly transmits power; and

a power receiving device that receives power from the power transmittingdevice,

wherein the power receiving device includes

-   -   a coil configured to be used to receive power from an external,    -   a resonant circuit configured to include at least the coil, and    -   a detecting section configured to superimpose a measurement        signal for measuring a Q-factor of the resonant circuit on a        power transmission signal transmitted to the coil in a        contactless manner and remove the power transmission signal from        an alternating-current signal obtained by superimposing the        measurement signal on the power transmission signal, the        detecting section measuring the Q-factor by using the        alternating-current signal from which the power transmission        signal is removed.        (17)

The contactless power transmission system according to (16), wherein

the detecting section includes

-   -   a resonant frequency adjuster that is connected to the resonant        circuit and is to change resonant frequency of the resonant        circuit from a first frequency to a second frequency different        from the first frequency,    -   a first frequency remover that does not allow passage of an        alternating-current signal with the first frequency and allows        passage of at least an alternating-current signal with the        second frequency, and    -   a Q-factor measuring section that calculates the Q-factor by        using the alternating-current signal that has passed through the        first frequency remover and includes the measurement signal.        (18)

A detecting method including:

superimposing a measurement signal for measuring a Q-factor of aresonant circuit including at least a coil on a power transmissionsignal transmitted to the coil in a contactless manner by a detectingsection included in a detecting device;

removing the power transmission signal from an alternating-currentsignal obtained by superimposing the measurement signal on the powertransmission signal; and

measuring the Q-factor by using the alternating-current signal fromwhich the power transmission signal is removed.

(19)

The detecting method according to the above-described (18), wherein

the power transmission signal is an alternating-current signal with afirst frequency and the measurement signal is an alternating-currentsignal with a second frequency different from the first frequency, and

a resonant frequency adjuster included in the detecting section isconnected to the resonant circuit to change resonant frequency of theresonant circuit from the first frequency to the second frequency.

The series of processing in the above-described embodiment examples canbe executed by hardware and can also be executed by software. In thecase of executing the series of processing by software, it can beexecuted by a computer in which a program configuring the software isincorporated in dedicated hardware or a computer in which a program forexecuting various kinds of functions is installed. For example, it canbe executed by installing a program configuring the desired software ine.g. a general-purpose personal computer.

A recording medium in which the program code of software to realize thefunctions of the above-described embodiment is recorded may be suppliedto a system or a device. Furthermore, it is obvious that the functionsare realized also through reading and running of the program code storedin the recording medium by a computer (or control device such as a CPU(central processing unit)) of the system or the device.

As the recording medium for supplying the program code in this case,e.g. the following media can be used: flexible disc, hard disc, opticaldisc, magneto-optical disc, CD-ROM, CD-R, magnetic tape, non-volatilememory card, and ROM.

Furthermore, the functions of the above-described embodiment arerealized by executing the program code read out by the computer. Inaddition, an OS (operating system) or the like operating on the computerexecutes part or all of actual processing based on an instruction ofthis program code. The case in which the functions of theabove-described embodiment are realized by this processing is alsoincluded.

In the present specification, the processing steps that describetime-series processing encompass not only processing executed in atime-series manner along the described order but also processing that isnot necessarily processed in a time-series manner but executed inparallel or individually (e.g. parallel processing or processing by anobject).

It is obvious that the present disclosure is not limited to theabove-described respective embodiments and other various modificationexamples and application examples can be employed without departing fromthe gist set forth in the scope of claims.

Specifically, the examples of the above-described respective embodimentsare preferred specific examples of the present disclosure and thereforeare given various limits that are technically preferable. However, thetechnical scope of the present disclosure is not limited to these modesunless a description to the effect that the present disclosure islimited particularly exists in the respective explanations. For example,materials used, the amounts of use thereof, processing times, processingorders, numerical conditions of the respective parameters, etc. employedin the above description are merely preferred examples, and dimensions,shapes, and arrangement relationships in the respective drawings usedfor the description are also schematic.

The present disclosure contains subject matter related to that disclosedin Japanese Priority Patent Application JP 2011-261816 filed in theJapan Patent Office on Nov. 30, 2011, the entire content of which ishereby incorporated by reference.

What is claimed is:
 1. A detecting device comprising: a coil configuredto be electromagnetically coupled to an external; a resonant circuitconfigured to include at least the coil; and a detecting sectionconfigured to superimpose a measurement signal for measuring a Q-factorof the resonant circuit on a power transmission signal transmitted tothe coil in a contactless manner and remove the power transmissionsignal from an alternating-current signal obtained by superimposing themeasurement signal on the power transmission signal, the detectingsection measuring the Q-factor by using the alternating-current signalfrom which the power transmission signal is removed.
 2. The detectingdevice according to claim 1, wherein the power transmission signal is analternating-current signal with a first frequency and the measurementsignal is an alternating-current signal with a second frequencydifferent from the first frequency.
 3. The detecting device according toclaim 2, wherein the detecting section includes a resonant frequencyadjuster that is connected to the resonant circuit and is to changeresonant frequency of the resonant circuit from the first frequency tothe second frequency, a first frequency remover that does not allowpassage of the alternating-current signal with the first frequency andallows passage of at least the alternating-current signal with thesecond frequency, and a Q-factor measuring section that calculates theQ-factor by using the alternating-current signal that has passed throughthe first frequency remover and includes the measurement signal.
 4. Thedetecting device according to claim 3, further comprising a separatorconfigured to be connected to a side to which a load on an opposite sideto at least the coil across the resonant circuit is connected, andelectrically separate the load from the resonant circuit when thedetecting section measures the Q-factor.
 5. The detecting deviceaccording to claim 4, further comprising a power storage configured tobe charged with at least power consumed in measurement of the Q-factorin the detecting section by using the power transmission signal receivedby the coil from the external, wherein the detecting section measuresthe Q-factor by using the power stored in the power storage in a periodwhen connection between the resonant circuit and the load is set off. 6.The detecting device according to claim 3, further comprising a secondfrequency remover configured to be connected to a side to which a loadon an opposite side to at least the coil across the resonant circuit isconnected, and allow passage of the alternating-current signal with thefirst frequency, the second frequency remover not allowing passage of atleast the alternating-current signal with the second frequency.
 7. Thedetecting device according to claim 3, wherein the resonant frequencyadjuster includes at least either a capacitor or a coil and is connectedbetween the resonant circuit and the first frequency remover.
 8. Thedetecting device according to claim 3, further comprising a determiningsection configured to compare the Q-factor obtained by the Q-factormeasuring section with a reference value set in advance to determine astate of electromagnetic coupling between the coil and the external. 9.The detecting device according to claim 8, wherein the state ofelectromagnetic coupling between the coil and the external is whether ornot a conductor near the coil or a circuit including any coil exists.10. The detecting device according to claim 3, wherein the Q-factormeasuring section acquires a first voltage applied between both ends ofthe coil configuring the resonant circuit and the resonant frequencyadjuster and a second voltage applied between both ends of the coil fromthe alternating-current signal that has passed through the firstfrequency remover, and calculates the Q-factor from a ratio between thefirst voltage and the second voltage.
 11. The detecting device accordingto claim 3, wherein the Q-factor measuring section calculates theQ-factor by using a half width method in which the Q-factor is obtainedfrom a band corresponding to √2 times an absolute value of impedance ofa series resonant circuit including at least the coil at resonantfrequency.
 12. The detecting device according to claim 3, wherein theQ-factor measuring section calculates the Q-factor by using a half widthmethod in which the Q-factor is obtained from a band corresponding to1/√2 times an absolute value of impedance of a parallel resonant circuitincluding at least the coil at resonant frequency.
 13. The detectingdevice according to claim 3, further comprising a communication sectionconfigured to transmit the Q-factor measured by the detecting section toa power transmission side of the power transmission signal.
 14. A powerreceiving device comprising: a coil configured to be used to receivepower from an external; a resonant circuit configured to include atleast the coil; and a detecting section configured to superimpose ameasurement signal for measuring a Q-factor of the resonant circuit on apower transmission signal transmitted to the coil in a contactlessmanner and remove the power transmission signal from analternating-current signal obtained by superimposing the measurementsignal on the power transmission signal, the detecting section measuringthe Q-factor by using the alternating-current signal from which thepower transmission signal is removed.
 15. The power receiving deviceaccording to claim 14, wherein the detecting section includes a resonantfrequency adjuster that is connected to the resonant circuit and is tochange resonant frequency of the resonant circuit from a first frequencyto a second frequency different from the first frequency, a firstfrequency remover that does not allow passage of an alternating-currentsignal with the first frequency and allows passage of at least analternating-current signal with the second frequency, and a Q-factormeasuring section that calculates the Q-factor by using thealternating-current signal that has passed through the first frequencyremover and includes the measurement signal.
 16. A contactless powertransmission system comprising: a power transmitting device thatwirelessly transmits power; and a power receiving device that receivespower from the power transmitting device, wherein the power receivingdevice includes a coil configured to be used to receive power from anexternal, a resonant circuit configured to include at least the coil,and a detecting section configured to superimpose a measurement signalfor measuring a Q-factor of the resonant circuit on a power transmissionsignal transmitted to the coil in a contactless manner and remove thepower transmission signal from an alternating-current signal obtained bysuperimposing the measurement signal on the power transmission signal,the detecting section measuring the Q-factor by using thealternating-current signal from which the power transmission signal isremoved.
 17. The contactless power transmission system according toclaim 16, wherein the detecting section includes a resonant frequencyadjuster that is connected to the resonant circuit and is to changeresonant frequency of the resonant circuit from a first frequency to asecond frequency different from the first frequency, a first frequencyremover that does not allow passage of an alternating-current signalwith the first frequency and allows passage of at least analternating-current signal with the second frequency, and a Q-factormeasuring section that calculates the Q-factor by using thealternating-current signal that has passed through the first frequencyremover and includes the measurement signal.
 18. A detecting methodcomprising: superimposing a measurement signal for measuring a Q-factorof a resonant circuit including at least a coil on a power transmissionsignal transmitted to the coil in a contactless manner by a detectingsection included in a detecting device; removing the power transmissionsignal from an alternating-current signal obtained by superimposing themeasurement signal on the power transmission signal; and measuring theQ-factor by using the alternating-current signal from which the powertransmission signal is removed.
 19. The detecting method according toclaim 18, wherein the power transmission signal is analternating-current signal with a first frequency and the measurementsignal is an alternating-current signal with a second frequencydifferent from the first frequency, and a resonant frequency adjusterincluded in the detecting section is connected to the resonant circuitto change resonant frequency of the resonant circuit from the firstfrequency to the second frequency.